The present invention relates to a thickness gauge for use in connection with measuring the skeleton remaining after a blanking operation. More particularly, the thickness gauge is carried with the press ram adjacent to the die for movement in order to measure the blanked skeleton during each stroke of the press. Prior art thickness measuring devices include techniques which measure the sheet stock material before blanking. Such devices are used to avoid problems associated with varying stock thickness. It is known that in metal sheet materials, the thickness across the surface tends to vary as a result of the casting and rolling operations necessary for manufacturing sheet. Thickness varies along lines parallel and perpendicular to the roll axis. Recognizing that the thickness varies laterally across a given section of the web of sheet material, it is important that the thickness gauge be compact and inexpensive enough to be used for monitoring the thickness at various points laterally across the web. Prior art thickness gauges are expensive and are rarely used to measure the web at more than one longitudinal span. It is also important to be able to measure the thickness of the sheet at a point which is close to the die set, such that, an accurate measure of the material thickness for any blank can be obtained.
Prior art thickness gauges have necessitated a separate apparatus for holding and supporting such gauges apart from the press, whereby the sheet being fed into the press was first passed through the thickness gauge before it entered the press. Such commonly used thickness gauges can rely, for example, on a pair of juxtaposed roller wheels which define and measure the sheet thickness by means of the spacing between their axes. Such a thickness measuring device is disadvantageous because the thickness of a particular sheet section is not easily relatable to a particular blank formed on the press and because the wear on the rollers tends to double the error in the reading.
It is, therefore, an object of the present invention to provide a thickness gauge which is carried with each press stroke in order to measure the thickness of the material being blanked so that each measurement can be associated with a particular blank formed by the press.
It is an object of the invention to provide a non-contact type transducer which can be remotely mounted for measuring the distance to a target also remotely mounted whereby the transducer is protected from the movement of sheet through the press and the transducer is insensitive to variations in the type of material being measured due to lack of homogeneity in a given material, to variations in surface plating, and to surface roughness.
It is still another object of the invention to provide a thickness gauge which will accommodate an overstroke of the device without deleterious consequences to the thickness measuring components.
It is a further object of the invention to provide a thickness gauge which permits relative motion between the reference detecting pins and the measuring or feeler plunger of the gauge whereby varying thicknesses of the sheet material will not harm or damage the thickness transducers which are sensitive to 0.00254 mm.
It is yet another object of the invention to provide a thickness gauge which is compact, inexpensive and reliable such that it can be mounted and carried with the press for movement with the die or punch during blanking.
For a device of such accuracy which is relatively low in cost, easy to adapt to any press any extremely flexible with regard to its application, the present thickness gauge uses the rigidity and the machine cycle of the cupping press to save the space and the cost of a separate machine. Each sinusoidal press ram motion lifts the feeler and the pins away from sheet stock during its advance through the machine. This motion prevents damage due to jamming, wearing due to sliding or rolling contact because the motion of the sheet stock occurs after the press stroke has retracted the gauge from its proximity to the stock. Similarly, there is immunity to burrs, welds and other surface imperfections often found on the sheet stock. Mounting of the gauge to the press ram eliminates the need to move the thickness gauge out of the way during press threading, press cleaning or press jam clearing operations.
A reference plane can be established by a portion of the press or by a special segment specifically added to the press at its working plane on the bolster plate, bed or platten across which the stock moves. While it is preferred it is not essential that the reference planes be perfectly aligned with the vertical axis of the gauge since the centerline of the feeler is always perpendicular to the reference plane and the three reference pins can in tripod fashion accommodate different heights relative to the press bolster plate, bed or platten without affecting the accuracy of the thickness measurements. To a certain extent there is compensation for changes due to wear or thermal expansion since both the feeler and the pins receive similar treatment during use.
The explanation of the details, features and advantages of the present invention will be better understood by reviewing the summary and the detailed description of the invention.